Briones Regional Park
Briones is 5000 acre park in Northern California. When we lived in Pleasant Hilll it was about 3 miles from my house, I could ride there on my bike in about 15 minutes and drive there in 5. I enjoyed riding my bike along the trails, and went hiking every Friday along the Blue Oak trail up to Tabletop. You can view more info about Briones itself in the resources page.
Hikes and Bike Rides